Numerous means have been sought to improve the fuel-efficiency of moving bodies and, especially, moving bluff bodies by reducing their aerodynamic drag. In the field of surface transportation and, particularly in the long-haul trucking industry, even small improvements in fuel efficiency can reduce annual operating costs significantly. It is therefore advantageous in the design of a vehicle to reduce drag forces, thereby increasing the aerodynamic properties and efficiency of the vehicle.
The over-the-highway cargo-hauling tractor-trailer combination is one vehicle that experiences excessive aerodynamic drag. Generally described, tractor-trailer combinations typically include a tractor 18 having a so-called fifth wheel by which a box-like semi-trailer 24 may be attached to the tractor 18 by an articulated connection for transportation of the cargo trailer, as shown in FIG. 1. The shape of the conventional cargo trailer is essentially a rectangular box having a flat, rectangular roof 38 and matching floor 40, along with flat, rectangular side panels 42. The fore and aft vertical surfaces 44 and 46 of such trailers are also generally flat rectangular surfaces. The aft section of the trailer 24 is supportably mounted on one or more wheel assemblies, illustrated as 52 and 54.
Most large long-haul cargo trailers similar to those described above exhibit less than optimal aerodynamic performance during highway operation. At highway speeds, these conventional trailers develop a substantial amount of turbulent airflow in the region between the axles of the wheel assembles below the trailer box. This turbulence results in significant aerodynamic drag, increasing both fuel consumption and Nitrogen Oxide (NOx) emissions of the tractor 18.